Thorough Comparison Between iPhone 2G and 3G
This is the second article that detailed the internal structure of the "iPhone 3G." Based on the first story, in which we torn down the iPhone 3G, we compared it with the previous model, iPhone 2G. We found Apple's measures to enhance the workability and reduce the mounting area and cost in various areas.
The "iPhone 3G," a third-generation (3G) mobile phone of Apple Inc, was released July 11, 2008, in 22 countries. Nikkei Electronics broke down an iPhone 3G released in Japan with the help of engineers from a Japanese parts manufacturer. We compared its components with those of the iPhone 2G, which was released in the US June 29, 2007, for analysis.
The appearance of the iPhone 3G is almost identical to that of the 2G model. However, its inside, including the parts layout, is totally different. We could see that assembly workability was improved and some measures were taken to reduce the mounting area as well as parts costs.
On the other hand, the electrical circuit seems to have been designed in line with the previous model, judging from the fact that most of the parts mounted on the main board are supplied by the manufacturers of the 2G model parts.
Parts laid out with considerations for workability
The outside dimensions of the handsets are almost the same, 115.5 x 62.1 x 12.3mm for the iPhone 3G and 115 x 61 x 11.6mm for the 2G model. In respect to functionality, the differences are limited to some mobile phone functions such as W-CDMA/HSDPA and GPS reception functions.
However, when we disassembled the two models, we saw big differences in terms of internal layout (Fig 1). The iPhone 2G had its main parts laid out on both sides of a metal frame in the central area of the chassis. The main board and the connector for external connection are positioned far from each other, and a flexible substrate for connecting them was wound inside the chassis.
In contrast, the parts were simply accumulated on the chassis cover in the iPhone 3G. It has one main board and the flexible substrate for connecting other modules is short. It is clear that the assembly workability was enhanced.
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The employment of the resin back cover improved flexibility of antenna layout in the iPhone 3G. The main antenna for W-CDMA and GSM is mounted on the bottom of the chassis, while the sub-antenna for wireless LAN, Bluetooth and GPS is mounted on the upper part of the chassis.
"Antennas should be located as far as possible from each other to prevent radio wave interference," said an engineer from a Japanese parts manufacturer. "They probably wanted to enhance the performances including sensitivity."
As for the iPhone 2G, the back cover of the chassis is composed of two parts, one made of metal and the other made of resin. And the antennas are concentrated on the bottom of the chassis, where the resin cover is located.
As a result of this structure, two long coaxial cables had to be used inside the chassis in order to connect the main board located at the upper part of the chassis to the antennas. The cables were grounded to prevent noise.
Moreover, the positional relation between the main board and the Li-polymer secondary battery was changed. In the iPhone 3G, the single-structure main board is placed on top of the Li-polymer secondary battery. This layout made it possible to create contact points on the main board for connecting the secondary battery and antennas (main and sub) to the main board.
In the iPhone 2G, the main board, the Li-polymer secondary battery and the antennas were positioned side by side. The main board was connected to the secondary battery by soldering three cables.
Cost reduced by using same manufacturers
Unlike its predecessor, the iPhone 3G has a single main board, and the main parts are concentrated on one side of the board. Comparing their parts on a functional basis, we found that Apple uses the same suppliers for most of the parts (Note 1). In particular, there were surprisingly fewer differences in the block related to application functions than in the wireless circuit block.
In the iPhone 2G, the main board was separated into a block for application functions and one for the wireless circuit. One engineer said, "I got the impression that the iPhone 2G was created by forcefully combining the main board of a music player such as the iPod with a mobile phone main board."
Note 1: iSuppli Corp estimates the production cost of the 8-Gbyte iPhone 2G at US$265.83 as of June 2007, while that of 8-Gbyte iPhone 3G is estimated at US$174.33 as of July 2008.
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Meanwhile, the area of the main board in the iPhone 3G is about 1.5 times larger than the combined area of the two main boards in the 2G. When the main boards are compared in each circuit block, the mounting area of the newly-introduced RF processing circuit that supports 3G was increased by about 1.6 times.
The increased space was offset by the downsizing and modularization of the parts. For example, the transceiver circuits for wireless LAN and Bluetooth were replaced by a module manufactured by Murata Manufacturing Co Ltd, reducing the mounting area by about 60%.
In addition, the 3D acceleration sensor of STMicroelectronics, a joint venture of Italian and French companies, and the USB power supply control/charging control IC of Linear Technology Corp were downsized without changing their functions to reduce the mounting areas.
Furthermore, the outside dimensions of the application processor equipped with the ARM core, which carries the Apple logo and is supplied by Samsung Electronics Co Ltd, was downsized from 14 x 14mm to 13 x 13mm.
"They seem to have used the parts from the same suppliers to reduce costs and shorten the time required for the verification process," the engineer said.
Many modifications found on chassis covers
Many modifications were made to the designs that determine the appearance of the product. As mentioned earlier, the iPhone 3G uses a resin back cover for the chassis so as to provide flexibility for the layout of the antennas, while the iPhone 2G used metallic back cover. The use of a resin back cover seems to have contributed to a reduction in cost as well as the flexibility of the antenna layout.
However, the back cover of the iPhone 3G is reinforced by a metallic frame, and there is a trace of cutting work applied after molding. Cutting work increases manufacturing cost. But "external distortion of the chassis can be minimized by applying cutting work, compared with a product that is simply press-molded," said an engineer from a Japanese device manufacturer. This cutting work is probably showing the Apple's commitment to the external appearance.
In contrast, Apple seems to have put a priority on cost reduction when making modifications to the front cover (display area) of the chassis. In the display area of the iPhone 3G, the front cover, the touch panel and the LCD panel are separately mounted.
In the iPhone 2G, the chassis cover, the LCD panel and the touch panel were adhered together with resin. By laminating the parts, reflections of outside light and the backlight are reduced, and the display performance is improved compared with the method in which a layer of air is created between the LCD panel and the touch panel.
"But the panel bonding process that uses resin has a problem with the yield," the engineer said. "In this aspect, even the appearance-oriented Apple seems to have placed priority on cost."